The present invention relates to a scroll compressor including means for eliminating over-compression.
A scroll compressor is a constant-volume type compressor in which the ratio between the volume at which a gas is sucked and the volume to which the gas is finally compressed is constant. Therefore, when this type of compressor is operated at a compression ratio smaller than a predetermined set value, the pressure in the compression chamber becomes higher than the discharge pressure to be obtained. This phenomenon is generally referred to as "over-compression". The over-compression unnecessarily loads the compressor resulting in an uneconomical consumption of driving power.
The over-compression can be avoided by an arrangement wherein the gas in the compression chamber is relieved to the discharge side of the compressor when the pressure in the compression chamber has become higher than the discharge pressure of the compressor. An example of such an arrangement is disclosed in, for example, U.S. Pat. No. 4,389,171. This patent, however, does not disclose critical design conditions necessary for preventing over-compression over the entire period of compression, i.e., from the moment at which the suction of the gas is completed to the moment at which the compression is finished, such as the positions of gas relief ports with respect to the number of turns of the scroll wrap, the number of the gas relief ports and the construction of valve means for selectively opening and closing these relief ports. Thus, the arrangement disclosed in the above-mentioned United States patent can prevent over-compression over only a limited portion of the entire compression period and cannot be applied to compressors for air-conditioners each of which have a small number of turns of the scroll wrap and to refrigerator compressors each of which have a large number of turns of the scroll wrap.